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Surface sulfurization of Cu(In,Ga)Se2 (CIGSe) absorbers is a commonly applied technique to improve the conversion efficiency of the corresponding solar cells, via increasing the bandgap towards the heterojunction. However, the resulting device performance is understood to be highly dependent on the thermodynamic stability of the chalcogenide structure at the upper region of the absorber. The present investigation provides a high-resolution chemical analysis, using energy dispersive X-ray spectrometry and laser-pulsed atom probe tomography, to determine the sulfur incorporation and chemical re-distribution in the absorber material. The post-sulfurization treatment was performed by exposing the CIGSe surface to elemental sulfur vapor for 20 min at 500°C. Two distinct sulfur-rich phases were found at the surface of the absorber exhibiting a layered structure showing In-rich and Ga-rich zones, respectively. Furthermore, sulfur atoms were found to segregate at the absorber grain boundaries showing concentrations up to ~7 at% with traces of diffusion outwards into the grain interior.
A fundamental problem in avalanche science is understanding the interaction between frictional processes taking place at the basal running surface and dissipative mechanisms within the avalanche body. In this paper, we address this question by studying how kinetic energy is dissipated into heat in snow avalanches. In doing so we consider the effect of random granular fluctuations and collisions in depth-averaged snow avalanche models. We show that relationships between the size of the granular fluctuations and the energy dissipated by granular collisions can be obtained by studying the energy input required to maintain steady-state flows. The energy input for granular fluctuations comes from mechanisms operating in the basal layer. The kinetic energy of the flow at the basal layer is converted to granular agitation energy, a random kinetic energy, which in turn is dissipated as heat by both viscous shearing and inelastic collisions at higher levels in the avalanche profile. Thus granular fluctuations play a crucial role in understanding the total dissipation process. We apply our theoretical considerations to develop a constitutive model for dense snow avalanches and are able to accurately model steady-state velocity profiles of both snow-chute experiments and field measurements.
We have built a Shectman-type photon-counting spectrometer based on the Latham-Geary “Z-Machine” design. The system is innovative in that the entire system rides on the telescope and communicates to the outside world via standard serial lines. Microprocessor architecture, memory controllers and new interconnect and packaging technologies have been employed. The system is portable and can be easily connected to almost any computer. It is suitable for calibrated spectrophotometry on a smaller telescope as well as for conventional spectroscopy.
In this work we compare ZnS-based buffer layers prepared by atomic layer deposition, ALD, and chemical bath deposition, CBD. Both material and device properties are compared. CBD buffer layers are amorphous with a Zn(OH,S) composition while ALD buffer layers used in devices are crystalline with a Zn(O,OH,S) composition. Devices with ALD buffer layers are stable while for CBD, large lightsoaking effects are seen. Stable devices with CBD buffer layers are obtained by including an ALD-(Zn,Mg)O layer on top of the CBD layer.
Co-evaporated CuIn0,5Ga0,5Se2 thin film solar cells were grown using a sequential Cu-Poor/Rich/Poor process (CUPRO). During the growth process, the substrate temperature was either kept constant at 570 °C (iso-CUPRO) or decreased during the first step to either 360 or 430 or 500 °C (bi-CUPRO). According to atomic force microscopy (AFM) measurements, the lower the temperature is in the first step the smoother the final CIGS surface becomes. By decreasing the first step temperature, cross-section scanning electron microscopy (SEM) and θ-2θ x-ray diffraction (XRD) do not reveal clearly any important changes of morphology and crystallographic preferred orientation. SLG/Mo/CIGS/Buffer layer/i-ZnO/ZnO:Al/grid(Ni/Al/Ni) solar cells with either a chemical bath deposited CdS or an atomic layer deposited Zn(O,S) buffer layer were fabricated. For both buffer layers, the bi-CUPRO processes lead to higher efficiencies. Besides, using Zn(O,S), the electronic collection was improved for the infrared spectrum as well as for the ultraviolet spectrum. This resulted in efficiencies close to 14,5% for the Zn(O,S) cells.
Deposition of MgHx (MgH2 + Mg) thin films is performed using RF reactive sputtering in argon-hydrogen plasma. Films are characterized using x-ray diffraction (XRD), scanning electron microscopy, optical and resistivity measurements. Formation of crystalline MgH2 is confirmed by XRD, but the formation of some metallic Mg in the films could not be avoided. Increased H/Mg ratio by deposition at high hydrogen flow or high total pressure gives films that oxidize within days or weeks. Deposition at elevated substrate temperature results in improved crystallinity and stability. Initial studies of MgHx for silicon surface passivation are presented.
In this paper the development and flight testing of flapping-wing propelled, radio-controlled micro air vehicles are described. The unconventional vehicles consist of a low aspect ratio fixed-wing with a trailing pair of higher aspect ratio flapping wings which flap in counterphase. The symmetric flapping-wing pair provides a mechanically and aerodynamically balanced platform, increases efficiency by emulating flight in ground effect, and suppresses stall over the main wing by entraining flow. The models weigh as little as 11g, with a 23cm span and 18cm length and will fly for about 20 minutes on a rechargeable battery. Stable flight at speeds between 2 and 5ms–1 has been demonstrated, and the models are essentially stall-proof while under power. The static-thrust figure of merit for the device is 60% higher than propellers with a similar scale and disk loading.
DNA was extracted from specimens derived from the calcaneus of the Tyrolean Ice Man under
sterile conditions in a laboratory, where no DNA extractions and PCR experiments had been
performed before. Agarose gel electrophoresis and ethidium bromide staining did not reveal any
evidence of genomic DNA in the preparation obtained, indicating a high degree of DNA degradation.
Nevertheless, we performed PCR amplifications with this sample using primer pairs specific for HLA
class II alleles. HLA-DRB and DQB1 alleles were amplified in a nested PCR approach. In one of the
reactions, we observed a distinct amplification product, which we directly sequenced. By comparing
the obtained nucleotide sequence with a database of HLA alleles we assigned the HLA-DRB1*1402
type to the amplified sample. None of the investigators involved possesses this allele, indicating that
no contamination with modern DNA had occured. The HLA-DRB1*1402 allele is extremely rare in
Europe, but is common in Inuits and South American Indians and has previously only once been
identified in the laboratory.
Oxygen-deficient, tetragonal thin films of YBa2Cu3O6+x with x ≈ 0.25, quenched from the deposition temperature, change to the oxygenated, orthorhombic phase with x ≈ 1, between 200 °C and 400 °C in flowing oxygen. The transition is not reversible in flowing oxygen, and cannot be completely reversed by cooling in flowing argon. We do not observe a transition of the orthorhombic films to the tetragonal phase up to 800 °C in flowing oxygen. We observe that the major impurity phases to appear under nonoptimal annealing conditions are oriented phases of YcuO2 and BaCu2O2, with Y2BaCu2O5 and Y2Cu2O5 conspicuously absent. These conclusions have been drawn from a study that uses perturbed angular correlation spectroscopy to probe the local microstructure of the films.
Hot-wire anemometer measurements in a plane jet issuing at a harmonically oscillating angle into a moving air stream have been made to aid the understanding of oscillatory jet flows in general and flow past aerofoils with oscillating jet flaps in particular. The rates of velocity decay and jet spreading are shown to be greater and less, respectively, than those for a steady jet parallel to the air stream. The shapes of instantaneous velocity profiles and limited measurements of turbulence intensity are similar to those for a steady jet in a parallel air stream if a correction is made for the small velocity difference across the curved jet. The motion of the jet centre-line indicates that flow path lines are similar to those for a steady jet flap over a significant range of frequency of jet oscillation. Finally, a quasi-steady jet flap theory is proposed for an analytical description of the major flow features.
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